During the manufacture of several goods, raw materials may be required that are provided in the form of webs 2 wound onto cores 3 in roll form. For example, a manufacturing process to produce absorbent articles, such as diapers, training pants, feminine hygiene absorbent articles, incontinence absorbent articles, etc., may include materials wound on rolls such as, for example, layers of the absorbent article, elastics and components of the absorbent core.
In general, webs 2 unwound from rolls may have web 2 alignment issues during the manufacturing process. Some causes of web 2 alignment issues can include the properties of the web 2 material or the manner in which the web 2 material is wound onto the core. For example, as some web 2 materials are unwound from the roll, the web 2 material properties may allow a tendency for the web 2 material to either neck or curl, and/or fold upon itself in the cross direction of the web 2. In other situations, the web 2 material may be wound on a roll in such a manner where transverse movement of the web 2 is inherent as the web 2 is unwound from the roll. For example, web 2 material unwound from a level-wound roll 1b must traverse the roll length 5 which introduces a large amount of web 2 weave during the manufacturing process. Additionally, some webs 2 may have the tendency to fold upon themselves in the cross direction of the web 2 when the web 2 encounters a change of direction in the web 2 path, such as a 90 degree turn. In some instances, the web 2 may encounter a twist that has been incorporated into the web 2 path as a means to turn the web 2 or to reduce web 2 weave. In prior systems, the web 2 may have been twisted with the use of a long dead bar and an idler, or non-rotating dead bar. Twists incorporated into the web 2 path for some web 2 materials can cause web 2 instability that may contribute to the web 2 folding over on itself. Web 2 foldover can also cause machine stops in order to correct the web 2 path. It can be understood by one skilled in the art that web 2 alignment or instability issues that arise early in the unwinding of the web 2 affect the web 2 alignment throughout the remainder of the process. The detection of web 2 alignment issues towards the end of the manufacturing process also allows for continuation of the web 2 alignment issues throughout the manufacturing process.
Web 2 alignment or instability issues can impact the quality of the finished product, aesthetically or functionally. Components of the finished product originating from webs 2 that experience web 2 alignment issues may not be placed in the desired location of the finished product. Web 2 alignment and instability issues can also cause waste and delay in the manufacturing process when the machine speed is reduced in order to control the web 2 material for desired splicing of one roll to another roll or for desired placement of the web 2 material in the finished product, for example, a cut and placed component of the absorbent core, such as a liquid distribution layer as is known to one skilled in the art. As such, a need remains to detect the web 2 alignment issues of webs 2 as they are unwound from a roll early in the manufacturing process. A further need remains to correct the web 2 alignment issues of webs 2 as quickly as possible in the manufacturing process. An additional need remains to eliminate the need to twist the web 2 in the manufacturing process.